Solution mining and refining minerals



Jan. 14, 1969 c, H, JACOBY 3,421,794

SOLUTION MINING AND REFINING MINERALS Filed Sept. 27. 1966 Sheet of 7INVENTOR. 1

CHARLES H. JACOBY ATTORNEYS Jan. 14, 1969 c. H. JACOBY 1,

SOLUTION MINING AND REFINING MINERALS Sheet Filed Sept. 27. 1966 ynzuunump y My EVAPOPATO I N EN '1 0R.

CHARLES H. JACOBY A TTORNE'YS Jan. 14, 1969 c. H. JACOBY SOLUTION MININGAND REFINING MINERALS Shget 3 of '7 Filed Sept. 27. 1966 mm 6 E m H W VS T w 8 am 1 I h 22 26 2B 1 11 U :1 ffl mn wnmibrfi m LQJG wbSMP M MMUMaul.

Jan. 14, 1969 c. H. JA COBY 3,421,794

SOLUTION MINING AND REFINING MINERALS Filed Sept. 27. 1966 Sheet 4 of 7LI-701 an L MP ea a an.

INVENTOR.

1 CHARLES H. JACOBY ATTORNEYS Jan. 14, 1969 c. H. JACOB'Y 3,421,194

SOLUTION MINING AND REFINING MINERALS Filed Sept. ,27. 1966 Sheet 5 of v1 N VEN TOR.

CHARLES H. JACOBY 611M, 6W4, Q0444, QM

A TTORNE Y5 Jan. 14, 1.969

C. H. JACOBY SOLUTION MINING AND REFINING MINERALS Sheet 6 of? FiledSept. 27. 1966.

HaT O/L F02 .STRINGERS T0 HEAT EXCHANGER INVEN'TOR 'CHA RL ES H. JACOBYA TTORNEYS Jan. 14, 1969 c. H. JACOBY SOLUTION MINING AND REFININGMINERALS Sheet Filed Sept. 27, 1966 INVENTUR.

CHARLES H JACOBY Y. I i M MWMWWE, I s m 6 ii ATTORNEYS United StatesPatent 3,421,794 SOLUTION MINING AND REFINING MINERALS Charles H.Jacoby, Grosse Ile, Mich., assignor to International Salt Company, ClarkSummit, Pa. Filed Sept. 27, 1966, Ser. No. 582,352 U.S. Cl. 299-5 17Claims Int. Cl. E21b 43/28; E21c 41/08 ABSTRACT OF THE DISCLOSURE Someof the heat extracted at the earths surface incidental to winningcrystallized mineral from a high temperature saturated mineral solutionobtained by flowing solvent through a mineral deposit at great depth isused to (a) minimize temperature drop of the up-coming solution and (b)reduce the rate at which heat is extracted from the deposit.

This invention relates to the mining and refining of soluble minerals;and more particularly to the mining of sodium chloride or other solublemineral salts including impurities; the absolute and relativesolubilities of which vary with temperature and/or pressure changes.More specifically, the invention relates to a process somewhat similarto that disclosed in commonly assigned U.S. patent application Ser. No.516,621, filed Dec. 27, 1965, noW Patent No. 3,348,883 and presentlypending in the names of Charles H. Jacoby and John L. Ryon, J r.

The present invention relates to an improved process and means forrefining or purifying mineral salts as aforesaid, concomitant to themining thereof as distinguished for example from the processes disclosedin U.S. Patents Nos. 2,555,340 and 2,876,182. Briefly stated, the priorpatented processes involve the taking of raw impure or run-of-mine saltinto solution; heating the brine thus formed and making it into asuper-saturated salt solution; and then subjecting the solution toevaporating and cooling processes whereby recrystallized, purified,sodium chloride is obtained.

More specifically, as explained in the aforesaid patents,

salt such as mined rock salt, usually consists of sodium chloride to theextent of about 90% to 99%; the balance being impurities such assulphates, silicates, carbonates, etc.; calcium sulphate being theprincipal impurity. According to prior refining procedures, such impuresalts have been refined in some instances by treatment of salinesolutions obtained directly from wells, or from water-solutions producedby dissolving previously mined or otherwise produced impure saltsubstances in water or other suitable solvents. Then, purified saltshave been extracted from such solutions by the use of vacuum-evaporatorsystems.

In accordance with the aforesaid patents, advantage is taken of thephenomenon known as the inverse solubility of calcium sulphate inrelation to sodium chloride. The calcium sulphate content of the crudesalt which is fed into the system will remain substantially undissolvedunder certain conditions, and can be removed by filtration or otherknown methods of separation. In carrying out the system, impure 'salt isfirst dissolved in a brine saturating zone wherein the temperature andpressure are maintained substantially greater than in the evaporationzone. Then when the brine is delivered into the evaporation zone a dropin temperature takes place, with the result that the brine becomes orremains undersaturated with respect to the calcium sulphate even thoughthe concentration of the sodium chloride becomes substantiallyincreased. Or, alternatively, the purer sodium chloride may beprecipitated out of the solution at this stage, in ac- 3,421,794Patented Jan. 14, 1969 ICC cordance with the preferred practice. In suchcase any undissolved material, whether dirt or other undissolvedinclusions such as calcium sulphate, is separated from the brine beforethe brine is taken into the evaporation or recrystallizing zone, withthe result that the sodium chloride becomes separated from suchimpurities; and, if desired, it can then be precipitated out so as toprovide a product of high purity. According to such systems sodiumchloride of purities in excess of 99.98% can be produced directly from asource of relatively impure salt such as dirty rock salt.

The invention disclosed in the aforesaid copending application Ser. No.516,621 provides an improved combination salt mining and purifyingmethod and means, employing only some of the previously patentedpractices referred to above; whereby certain operating advantages accruein respect to the mining phase as well as in respect to the productbeneficiation phase of the overall operation.

However, it is specifically an object of the present invention toprovide still further improvements in operative systems and techniquesfor such purposes; whereby to realize plant completion investment andoperating economies.

Another object is to provide an improved system as aforesaid wherebyprecise operational control and efficiencies may be realized.

Other objects and advantages of the present invention will be apparentfrom the following specification and the accompanying drawing wherein:

FIG. 1 illustrates diagrammatically by way of a vertical sectional view,a geological formation including a typical salt dome in process of beingmined in accordance with the present invention;

FIG. 2 is a fragmentary enlarged scale composite view of portions ofFIG. 1, including a diagrammatic illustration of the surface-plantequipment of FIG. 1;

FIGS. 3, 4, are. enlarged scale diagrammatic illustrations of typicalwell completion apparatii such as may be employed in conjunction withthe production well casing head and foot sections respectively; inaccordance with the system of the invention;

FIGS. 5, 6, are enlarged scale sectional views taken as suggested bylines 5-5 and 66 respectively of FIGS. 3, 4;

FIGS. 7, 8, are views corresponding to FIGS. 3, 4, but showing amodified form of well completion arrangement such as may be employed inconjunction with the invention;

FIG. 9 is a sectional view taken as suggested by line 9-9 of FIG. 7; and

FIGS. 10, 11, are views corresponding to the bottom end portion of FIG.8 but showing modified forms of suitable well completion arrangements.

As shown by way of example herein, the invention is embodied in a systemfor simultaneously mining and purifying sodium chloride salt occurringin an underground deposit of the Well known salt dome type; but it is tobe understood that the invention may be usefully applied to other formsof soluble mineral deposits, such as sodium borate, potash, and thelike. However, it is a feature of the invention that the system thereofis particularly adapted for use in connection with mineral depositsoccurring at relatively great depths below the earth surface, employingas an incident thereto the ambient heat supply inherently existent atdeep levels underground. For example, it is known that undergroundtemperatures invariably increase with depth, and that in deep lying saltdomes for example, temperatures of the order of 240 F. have beenrecorded at depths of the order of 8,000 feet.

The present invention takes advantage of the fact that deposits of saltsuch as illustrated herein are at such depths that the earthtemperatures ambient to a borehole leading downwardly from the surfaceand penetrating such a deposit are of high order, and may furnish someof the heat supply requirements for a coincident beneficiation operationwhen employing apparatus of the present invention. Hence, substantialoperating economies are effected.

By way of more specific explanation, as illustrated herein a salt domeor other such deposit may for example be intersected by a verticalborehole as indicated generally at 15, which comprises a combinationinjection and production well opening from the earths surface into thesought-for mineral deposit. To complete the borehole and to preventcompression failures of the walls thereof, it will of course bepreferably cased as is well known in the art. As shown in FIGS. 3-7 theborehole is fitted with a casing system of the concentric quadruplecasing type, for purposes to be explained more fully hereinafter. Asshown in FIGS. 8, 10, 11, a triple casing system is shown. In any casethe borehole is drilled into the salt deposit so that at its nether orlower end it penetrates into the deposit. The multiple casing system ofthe borehole thus provides a system wherein solvent may be pumped downone of the casing annuli and brine delivered upwardly through another tothe surface plant. As is well known in the art, a dissolution cavity asillustrated at 16 for example in FIGS. 1, 2, 4, 8, 10, 11, willthereupon form in the salt deposit, from which saturated brine may becontinuously pumped to the surface plant which is indicated generally at20 (FIGS. 1, 2).

It is a particular feature of the present invention that the systemthereof utilizes the vast heat supplies existent at substantial depthsin the earths crust, to assist in the requisite vaporization and/ orbrine-evaporation phases of the salt product Ibeneficiation operation;and in addition to heat the solvent (comprising the residual brineeflfluent from the evaporation operation plus make-up fresh solventadded if and when needed) as it is injected through the borehole easinginto the dissolution cavity, thereby causing it to be delivered into thecavity in under-saturated condition. By circulating this under-saturatedsolvent mixture into the dissolution cavity and from thence back to thesurface and then through the salt recovery facility, under thespecifically controlled conditions of the present invention as will beexplained hereinafter, the salt deposit per se provides at the same timethe source of raw mineral and a source of a portion of the heat supplywhich is required in connection with the purification process at thesurface plant. When the system is installed and operated within thespecific parameters of the present invention, the heat so derived willbe so conserved and utilized as to render the system in every waypracticable; the abstraction of heat from the salt deposit beingautomatically compensated by continuous heat conduction replacementsfrom the ambient geology.

As mentioned hereinabove, the casing portion of the system asillustrated at FIGS. 37 is of the quadruple casing type; illustratedherein as including concentrically arranged casings of tubings 22, 24,26, 28. The primary (inner) conduit or tube 22 is provided to convey theproduct brine in heat-insulated form upwardly to the point of dischargeof the brine into the evaporator portion of the brine treatingapparatus. The present invention features an arrangement whereby theheated, saturated, brine derived from the dissolution cavity will bemaintained under optimum pressure and temperature conditions untildelivery to the evaporator; thereby preventing premature crystallizationof solids in the conduit system.

To accomplish this purpose of this invention a closedcircuit typeheat-exchange system is arranged in conjunction with the productionbrine casing 22. As best shown in FIGS. 3-6, the brine up-flow conduit22 and the next outer conduit 24 provide therebetween an annularpassageway into which heated water, or oil, or sulphur, or othersuitably fluid heat-conveying media may be injected, as from an inletconnection illustrated at 30 (FIG. 3), at the well head component of thewell. The casing 24 is packed at its bottom end as indicated at 32 (FIG.4) and perforated thereabove as shown at 33. The annular space betweenthe conduits 24 and 26 is arranged to provide a return passageway forthe heating fluid on its way back up to the heater 35 (FIG. 2). An exitconnection 36 (FIG. 3) is provided at the well head in conjunction withthe casing 26 to convey the return fluid to the heating apparatus.

The heater 35 may be of any suitable type commercially available heatexchanger employing any preferred form of heat energy source; such assteam from a stand-by-boiler or the like as indicated at 38. Also, thehot vapors efliuent from the evaporator operation may be fed to theheater apparatus as illustrated at FIG. 2, to effect heat supply costeconomies.

In any case, it is a particular feature of the present invention thatthe fluid heated by means of the apparatus 35 is circulated as by meansof a pump 40 through a closed-circuit system comprising essentially theannular spaces between the well casings 22-24 and 24-26. Therefore thecirculating fluid may be selected to provide certain preferred operativecharacteristics, such as being non-corrosive to the hardware coming incontact therewith, and/or free from precipitant-prone ingredients suchas would otherwise tend to scale the casing walls or other hardware.Hence substantial maintenance difl lculties and expense are avoided.

It is to be understood that the system of the invention may employ anypreferred form of salt extracting apparatus. For example, as shown inFIG. 2 herewith it may be of a relatively simple, single stage,evaporator" or recrystallizer type employing procedures disclosed forexample in US. Patents 2,555,340 and 2,876,182 wherein the brine issubjected to pressure and temperature drop conditions permitting puresolid salt to separate out from the brine. However it is to beunderstood that in lieu of the simple, basic form of extracting systemas suggested by FIG. 2 herewith, any other preferred multi-stage and/ ormore sophisticated recovery and/or refinery system (such as disclosed inthe aforesaid patents) may be employed.

In any case, the efiiuent residual brine from the recovery facility willpreferably be pumped back down the borehole through the annular spacedefined by the casings 26-28. This brine will be sodium chloridesaturated at its injection temperature (except perhaps wheneverevaporation losses require the addition of make-up solvent which may befurnished at somewhat lower temperature). However, as explainedhereinabove, as this brine travels downwardly through the uninsulatedcasing 28 in heatexchange relation therewith, it becomes heated; such asby example from an injection temperature of the order of say F. up to atemperature of the order of 220 F. as it traverses the dissollutioncavity; assuming the cavity ambient rock temperature to be of the orderof 240 F. Because the, brine upflow conduit 22 is maintained a hightemperature as explained hereinabove, when the superheated (andtherefore supersaturated) brine or other solution reaches the evaporatorapparatus it may well be of a temperature in the order of 215 F., ormore. The resistance to fluid flow offered by the extended casingstructures will of course insure to some extent that the dissolutionproduct is also maintained under high pressure until it is dischargedinto the evaporator apparatus. However, if preferred, a fiow restrictiveorifice may be employed at the discharge point to maintain the desiredback-pressure on the system. Hence, it will be appreciated that theoperative characteristics of the solute heating and saturating phase ofthe system of the invention bring it well within the realm offeasibility for realization of the objects of the invention as set forthhereinabove.

Another technological feature of the system of the invention resultingin improved performance and economic advantages is that by virture ofthe operative relationships of the essential components of the system,there is no essential need for certain accessory devices such as arecalled for by prior art systems. This derives from the fact thatinsoluble impurities resident in the deposit being mined, tend to settleout of the brine when released by dissolution of the cavity wallmaterial, and fall into and remain in the bottom of the cavity; andtherefore the impurity carry-up into the refining apparatus is minimal.Hence, the need for filtering equipment is minimized, and the need forpurifying equipment such as saturators, condensers, heaters and the likein connection with the surface plant may be eliminated or at leastminimized. Also, because in the case of the present invention theinsoluble impurities occurring in the mineral deposit are not brought tothe surface, there is no problem at the surface plant with respect todisposal of wastes.

It is also noteworthy that in the case of the present invention thephenomenon known as the inverse solubility ratios of sodium chloride andcalcium sulphate (the major impurity ingredient of native rock salt)operates within the dissolution cavity of the system. Because thesolvent liquid in the cavity is maintained a high temperature itautomatically retards dissolution of the undesirable calcium sulphateinto the brine. Therefore large percentages of this material whenreleased in situ from the salt deposit will simply settle down into thebottom of the dissolution cavity, thereby reducing the impurityseparation load on the surface plant. In fact, by virtue of this featureof the invention the surface refining plant requirements may well be soreduced that only a rudimentary form of solid salt recovery apparatusmay be satisfactorily employed.

As shown in FIGS. 7, 8, 9, the conduit system for circulating theheating fluid in heat-exchange relation to the brine delivery conduitmay be of the so-called hanging string type, instead of the type shownin FIGS. 36. In this situation, the casing string 24 of FIGS. 36 isreplaced by a shorter hanging string 40 (FIG. 7) which is supportedsolely from the well head or Christmas tree structure as indicated at44. A heated fluid is then conveyed from the heat exchanger 35 (FIG. 2)through inlet connection 46 (FIG. 7) to travel down in heating relationaround the brine upfiow conduit 22 and thence around the open end of thehanging pipe 40 and then returning upwardly to exit through theconnection 48 for return to the heat exchanger.

In some situations if more precise brine temperature control may berequired, this may be attained by installing supplemental heating fluidsupply devices such as hanging tubes 50 (FIGS. 7, 8, 9, 10, 11). Thesemay be arranged to deliver heating fluid as through an inlet connection52 (FIG. 7), down to such depths (within the annulus defined by thetubes 22, 26) as may be found necessary to establish a uniformtemperature jacket around the brine conduit throughout its length,notwithstanding the existence of different temperature conditions and/or different heat conductivity characteristics at different levels ofthe ambient geology. Hence, the supplement heating tubes may preferablyterminate at the same or different elevations, as dictated by theunderground conditions encountered. Alternatively, the tubes may so beemployed to draw off at any desired elevations the fluid within theannulus, to thereby attain precise temperature control of the system.

- FIG. 11 also illustrates another form of well completion arrangementwherein the brine upfiow conduit 22 is disposed to rest at its bottomend upon the solution cavity floor, or within a previously drilledopening extending downwardly into the solid salt mass comprising thecavity floor. Thus, a substantial portion of the weight of the conduithardware will be carried by the foot of the structure, thereby relievingthe loads on the well head and/ or packing devices. Also, this systemwill operate to positionally stabilize the lower end of the casinghardware in the solution cavity. Although not illustrated herein, itwill of course be understood that either pneumatic or immiscible fluidpads may be employed to cover the top surface of the liquid occupyingthe dissolution cavity; thereby insulating the roof of the cavityagainst undesirable dissolution. By such means the dimensional progressof the dissolution cavity may be preferentially controlled, as is wellknown in the art.

It is of course in any case a requisite to practical operation of anysystem such as disclosed hereinabove that care be taken to insureagainst premature recrystallization of the solute within the ascendingcolumn of hot brine, such as would block up the conduit system andrender it inoperative. To prevent this, the ascending brine must be keptthroughout its travel within a narrow range of temperatures andpressures. In other words, until the brine is delivered to the surfaceplant, it must be maintained substantially at the temperature at whichthe supersaturated solution is created within the solution cavity.Hence, prior to initiation of an operative cycle, some portions of thegeological environment through which the brine solution will ascend, mayrequire to be preheated from some external heat supply source, so as tocreate a heat wall surrounding the entire brine production apparatus inorder to maintain the latter at substantially the temperature of thebrine in the solution cavity.

For example, for a period of weeks or perhaps months prior to starting aproduction operation, depending upon the heat conducting characteristicsof the ambient geology or other parameters, a supply of suitably heatedfluid such as steam, hot water, oil or the like may be circulated from aheat generator located at the surface plant through the hardware of thewell system, until an appropriate reservoir of heat surrounding the wellis established. This will insure that the ascending brine will bemaintained under the lowest possible heat loss conditions until it isdelivered to the surface facilities. Also, the conduit system at thesurface plant conveying the product brine to the recrystallizer orevaporator facilities will preferably be heat jacketed, to maintain thesolute temperature and thereby prevent premature crystallization of thesolute.

It will of course be appreciated that although only a few forms of theinvention have been illustrated and described in detail hereinabove,various changes may be made therein without departing from the spirit ofthe invention or the scope of the following claims.

I claim:

1. The method of concomitantly mining and beneficiating a deepunderground high-temperature deposit of soluble mineral includingimpurities disposed at such depth beneath the earths surface as to besurrounded by a hightemperature geological environment compared to theneighborhood earth surface rock temperature, to produce a relativelypure mineral product at the relatively low earth surface ambienttemperatures, said method comprising,

forming an access opening extending downwardly from the earths surfaceinto said deposit,

pumping a solvent liquid downwardly through said opening in directheat-exchange relation with the ambient geology thereby heating saidsolvent to an elevated temperature, and then directing said heatedsolvent to flow in dissolution-contact relation with saidhigh-temperature mineral to provide a highly concentrated hightemperature solution of mineral, and thence to flow upwardly throughsaid opening to a treating plant operating under substantially earthssurface temperature and pressure conditions, for separation of purifiedmineral from the impurities in said solution,

while simultaneously circulating and heating a heattransfer fluid in aclosed conduit system in heat exchange relation with said upfiowingmineral solution to insulate it from the ambient geology and maintainsaid solution at a prescribed high-temperature condition until deliveryto said treating plant.

2. The method as set forth in claim 1 wherein said mineral depositcomprises a sought-for ingredient having insolubility characteristicsvarying in direct relation to temperature changes and impurityingredients of inverse relation solubility characteristics, whereby theheated solvent passing through said deposit produces a dissolutionproduct having an improved ratio of pure vs impure ingredients fordischarge into said treating plant.

3. The method as set forth in claim 1 wherein said sought-for mineralingredient is of crystalline form and whereby when said purified mineralseparates from said dissolution product it precipitates inrecrystallized form.

4. The method as set forth in claim 1 wherein the liquid efliuent fromsaid treating plant is fed to said solvent pumping operation therebycomprising a portion of the make-up of said solvent.

5. The method as set forth in claim 4 wherein said solvent includes arelatively lower temperature fresh water make-up ingredient.

6. The method as set forth in claim 1 wherein said treating plantcomprises a series of evaporator devices, the liquid efliuent from eachsaid evaporator device comprising the feed input to the next succeedingevaporator device and the liquid eflluent from the last evaporator beingdelivered to the solvent make-up system for recirculation through thedissolution area and treating plant in closed circuit manner.

7. The method as set forth in claim 1 wherein said solution is passedupwardly through a first tube means and wherein said heat transfer fluidflows through second tube means positionally related concentrically ofsaid first tube means.

8. The method as set forth in claim 7 wherein said second tube meansterminates short of the lower reach of said first tube means, therebyconfining the heating effect on said solution of said heat-transferfluid to only an upper portion of the solution upflow system.

9. The method as set forth in claim 7 wherein said second tube meanscomprises a plurality of heat transfer fluid delivery t-ubes extendingdownwardly to dilferent levels underground thereby providingdifferential heat exchanging eifects progressively of the length of saidfirst tube means.

10. The method as set forth in claim 7 wherein said first tube meansrests at its bottom end upon the floor of the solution cavity therebyrelieving the tube suspension system of substantial portions of theweight thereof.

11. The method of concomitantly mining and beneficiating a deepunderground high-temperature deposit of soluble mineral includingimpurities disposed at such depth beneath the earths surface as to besurrounded by a high-temperature geological environment compared to theneighborhood earth surface rock temperature, to produce a relativelypure mineral product at the relatively low earth surface ambienttemperatures, said method comprising,

flowing solvent from the surface, through the deposit and back to thesurface at a rate to attain at the surface a saturated solutionsubstantially at the ambient temperature of the deposit,

simultaneously flowing a heat exchange fluid from the surface, towardthe deposit and back to the surface in a closed path in heat exchangerelation to the down-going solvent and upcoming saturated solution to(a) transfer heat to the down-going solvent while (b) minimizingtemperature loss of the up-coming saturated solution,

extracting heat from the saturated solution at the surface tocrystallize out some of the mineral at the surface,

and transferring some of said extracted heat to the heat exchange fluid.

12. The method of concomitantly mining and beneficiating a deepunderground high-temperature deposit of soluble mineral includingimpurities disposed at such depth beneath the earths surface as to besurrounded by a high-temperature geological environment compared to theneighborhood earth surface rock temperature, to produce a relativelypure mineral product at the relatively low earth surface ambienttemperatures, said method comprising,

flowing solvent from the surface, through the deposit and back to thesurface in a continuous path and at a rate to obtain a saturatedsolution at the surface substantially at the temperature and pressure ofthe deposit,

extracting heat from the saturated solution at the surface tocrystallize out some of the mineral therefrom,

removing the mineral crystals from the system,

and returning some of said extracted heat to the solvent flowingdownwardly to the deposit.

13. The method according to claim 12 wherein the last step includesflowing a heat exchange fluid in a closed path from the surface, towardthe deposit and back to the surface in heat exchange relation to saidsolvent.

14. The method according to claim 13 wherein said some of the extractedheat is transferred from the solvent system to the heat exchange fluidsystem at the surface.

15. The method according to claim 14 wherein exagenous heat is suppliedto the heat exchange fluid system at the surface.

16. The method according to claim 11 wherein the upcoming saturatedsolution is insulated from the ambient geology and said down-goingsolvent by said heat exchange fluid.

17. The method of concomitantly mining and beneficiating a deepunderground high-temperature deposit of soluble mineral includingimpurities disposed at such depth beneath the earths surface as to besurrounded by a high-temperature geological environment compared to theneighborhood earth surface rock temperature, to produce a relativelypure mineral product at the relatively low earth surface ambienttemperatures, said method comprising,

flowing solvent from the surface, through the deposit and back to thesurface in a continuous path and at a rate to obtain a saturatedsolution at the surface substantially at the temperature and pressure ofthe deposit,

extracting heat from the saturated solution at the surface tocrystallize out some of the mineral therefrom, removing the mineralcrystals from the system,

and utilizing some of said extracted heat to minimize temperature dropin the up-coming saturated solution as it flows from the deposit to thesurface.

References Cited UNITED STATES PATENTS 2,161,800 6/1939 Cross 299--53,022,986 2/1962 Brandt 299-5 3,205,012 9/1965 Dancy 299-5 X ERNEST R.PURSER, Primary Examiner.

